Praeger — On the Eaised Beaches of N.E. Ireland. 49 



the large increase of southern shells is accompanied by a slight 

 further decrease of northern types, till before the next period the mean 

 curve, indicating the general character of the fauna, has crossed the 

 neutral line, and the fauna of the estuarine clays and raised beaches 

 is seen to be of distinctly southern aspect. This is, however, the 

 period of maximum dominance of the southern shells. Their number 

 is seen to rapidly diminish, while the northern element remains 

 almost the same, so that at the present day the neutral line has been 

 again passed, and the fauna has assumed a slightly northern aspect. 



A cause for this recent collapse of the southern fauna of the north- 

 eastern seas has not, so far as I am aware, been suggested, nor have I 

 any explanation to offer. It may be pointed out that the north-east 

 of Ireland has, at present, the most northern moUuscan fauna of any 

 portion of the country, and this, as the diagram shows, is caused by 

 the extinction of southern forms rather than by the immigration of 

 northern ones. 



The present Paper may j&ttingly conclude with a detailed account 

 of a few of the more striking of these recent emigrations from the 

 district. It is to be noted that the north-eastern part of Ireland is, 

 both zoologically and botanically, the most boreal. The mild in- 

 fluences which characterize the western coast extend right up to the 

 most northerly point of Donegal and of Ireland ; and both fauna and 

 flora, terrestrial and marine, attain their most northerly aspect only 

 when we turn southward round Malin Head, and reach the counties of 

 Derry and Antrim. In accordance with this statement, it will be 

 seen that some of the shells about to be mentioned, which have now 

 forsaken the north-eastern shores, or show a striking diminution in 

 numbers, still flourish in the milder climate of Donegal, which is 

 actually further to the northward ; while, on the other side, their line 

 of retreat has been down the east coast towards Dublin. 



Lima Mans, Gmel. In the estuarine clay period lived in immense 

 abundance in Lame Lough, and more sparingly in Belfast Lough, 

 and off Portrush. Now almost extinct in the district, a very 

 few specimens only having been dredged ; lives in abundance in 

 Mulroy Bay, Co. Donegal, and sparingly off Dublin, but is not 

 recorded from the south or west. 



Tapes aureus^ Gmel. Its first appearance locally is in the boulder- 

 clay at Belfast Waterworks. It attains great abundance in the 

 estuarine clays and raised beaches, from Lame to Greenore. 

 As a living species it is extremely rare in the district, and in 

 Ireland has its headquarters in the west and south. 



K.I. A. PEOC, SEE. in., VOL. IV. ' E 



